The endorsements come with Kashkari, a former U.S. Treasury Department official, lagging in public opinion polls.

"Neel is the right candidate with the right message to challenge Gov. Brown, support Republican candidates up and down the ticket, and help us grow the Party in the long term," Wilson said in a prepared statement.

Gov. Jerry Brown, a popular Democrat, is widely expected to finish first in the June primary election, and Tim Donnelly, a tea party favorite, leads all Republicans in the race to finish second and advance to a runoff against Brown in the fall.

Kashkari, a moderate, hinted at a public appearance on Sunday that Romney's endorsement was coming. He also said former President George W. Bush "has been very helpful and made calls and opened doors."

While Kashkari has gained support from the Republican Party's political and consultant classes, he has struggled with the party's more conservative base. At a candidate forum in Anaheim on Sunday, the one question he was asked was if it was true he voted for Barack Obama in 2008.

Kashkari said he voted for Obama because he was getting better economic advice than the Republican nominee, John McCain.

"Yes, it is true," Kashkari said. "But I was definitely disappointed in President Obama and what he has done as president, and that's why I strongly supported Mitt Romney for president in 2012, and Mitt Romney is giving us a lot of help, too."